System for deploying the petals of a sectored mirror of an optical space telescope

ABSTRACT

A system is disclosed for deploying the petals of a sectored mirror assembly of an optical space telescope, wherein the sectored mirror includes a central hub and a plurality of petals disposed about the periphery of the central hub, and each petal has a petal root independently hinged to the central hub. The system includes a first hinge assembly having a root mount secured to a petal root and a hub mount secured the central hub, whereby the first hinge assembly affords the petal associated therewith freedom of rotation about a petal hinge axis. The system further includes a second hinge assembly including a root mount secured to the petal root and a hub mount secured to the central hub, whereby the second hinge assembly affords the petal associated therewith freedom of rotation about the petal hinge axis and freedom to expand and contract thermally, and move rigidly along the petal hinge axis in a frictionless, unconstrained manner. The system also includes a latch assembly including a clevis secured to the petal root at a location spaced from the hinge axis and a pair of laterally opposed latch mechanism operatively associated with the central hub for engaging the clevis upon rotation of the petal about the hinge axis from a stowed position to a deployed position.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The subject invention relates to a system for deploying thepetals of a sectored mirror of an optical space telescope, and moreparticularly, to a set of hinges for independently connecting a petal ofthe sectored mirror to the central hub of the sectored mirror and to alatch mechanism for securing the hinged petal to the central hub in adeployed position.

[0003] 2. Background of the Related Art

[0004] The success of the Hubble Space Telescope has spurred thedevelopment of other space-based astronomical observatories, includingsome incorporating a large diameter primary mirror. A number of designs,including the space-based observatory known as the Next Generation SpaceTelescope (NGST), have centered on a primary optic that is between sixand eight meters in diameter.

[0005] Several problems must be overcome to realize a space-basedastronomical observatory having such a large diameter mirror. Forexample, designs that propose a large diameter monolithic mirror wouldpresent significant manufacturing difficulties and risks. In addition,the size and shape of an observatory having a large diameter mirrorwould be constrained by the volume and shape of payload or cargo baysavailable on current launch vehicles.

[0006] Designs that propose a deployable large diameter mirror presentother problems. For example, to achieve a desired surface accuracy andoptical quality, the reflective components (e.g., sectors, segments orpetals) of the mirror must be aligned to a very high degree ofprecision, such as, within about 10 nanometers. In addition, because thespace-based observatory would experience broad thermal gradients, thethermal expansion and contraction of the deployable reflectivecomponents would need to be accommodated.

[0007] It would be beneficial therefore, to provide a deployment systemfor the reflective components of an optical space telescope thatexhibits a high degree of precision and accommodates thermal changesexperienced in an operational environment.

SUMMARY OF THE INVENTION

[0008] The subject invention is directed to a new and useful system fordeploying the petals of a sectored mirror assembly of an optical spacetelescope. The mirror assembly includes a central hub and a plurality ofpetals disposed about the periphery of the central hub. Each petal has apetal root that is independently hinged to the central hub of the mirrorassembly.

[0009] The petal deployment system of the subject invention includes afirst hinge assembly having a root mount secured to a petal root and ahub mount secured the central hub. The first hinge assembly is adaptedand configured to afford the petal associated therewith freedom ofrotation about a petal hinge axis.

[0010] The petal deployment system further includes a second hingeassembly having a root mount secured to the petal root and a hub mountsecured to the central hub. The second hinge assembly is adapted andconfigured to afford the petal associated therewith freedom of rotationabout the petal hinge axis, as well as freedom to expand and contractthermally, and move rigidly along the petal hinge axis in africtionless, unconstrained manner.

[0011] The petal deployment system further includes a latch assemblyincluding a clevis secured to the petal-root at a location spaced fromthe hinge axis and a pair of laterally opposed latches that areoperatively associated with the central hub for engaging the clevis uponrotation of the petal about the hinge axis from a stowed position to adeployed position.

[0012] Preferably, the first hinge assembly includes a first hinge shaftdisposed on the petal hinge axis. The first hinge shaft is secured tothe root mount of the first hinge assembly, and supports a plurality ofaxially spaced apart angular contact bearings. The angular contactbearings are formed from silicon nitride, do not require lubrication andare housed within the hub mount of the first hinge assembly.

[0013] Preferably, the second hinge assembly includes a second hingeshaft disposed on the petal hinge axis. The second hinge shaft issupported by the root mount of the second hinge assembly, and isdisposed within a cylindrical bearing cage. The bearing cage is formedfrom PTFE and retains a plurality of ball bearings. The ball bearingsare formed from silicon nitride and do not require lubrication. Thebearing cage is disposed between an inner bearing race and an outerbearing race, and is housed within the hub mount of the second hingeassembly.

[0014] Preferably, the latch assembly of the subject invention isadapted and configured to afford the petal associated therewith freedomto expand and contract thermally, and move rigidly along a latch axisextending parallel to the hinge axis in a frictionless, unconstrainedmanner. Each laterally opposed latch of the latch assembly includes alatch shaft mounted for linear movement along the latch axis. The clevisof the latch assembly defines a reception aperture for receiving thelaterally opposed latch shafts, and an actuator is operativelyassociated with each latch for moving the latch shaft thereof intoengagement with the clevis.

[0015] Each latch shaft is disposed within a cylindrical bearing cage,and each bearing cage is formed from PTFE. Each bearing cage retains aplurality of ball bearings formed from silicon nitride, and is disposedbetween an inner bearing race and an outer bearing race. Each bearingcage is housed within a hub mount secured to the central hub, and eachhub mount includes a base portion and a cylindrical housing portion.

[0016] These and other unique features of the petal deployment system ofthe subject invention will become more readily apparent from thefollowing description of the drawings taken in conjunction with thedescription of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] So that those having ordinary skill in the art to which thesubject invention appertains will more readily understand how toconstruct and use the petal deployment system of the subject invention,reference may be had to the drawings wherein:

[0018]FIG. 1 is a perspective view of an optical space telescope havinga primary mirror assembly that includes a hexagonal central hub portionand six petals with reflective surfaces independently hinged to thecentral hub portion, with each of the six petals disposed in a deployedposition;

[0019]FIG. 2 is a perspective view of the optical space telescope ofFIG. 1, wherein three of the petals are hingedly mounted to the centralhub portion and stowed in an aft position and three of the petals arehindgely mounted to the central hub portion and stowed in a forwardposition;

[0020]FIG. 3 is a side elevational view of a petal mounting section ofthe central hub portion of the optical space mirror of FIGS. 1 and 2, asviewed along the mounting surface of the petal root structure,illustrating in top plan view the double throw latch assembly of thesubject invention which is mounted on the central hub portion, andillustrating in side elevational view the two unique hinge assemblies ofthe subject invention which are mounted to the petal root structure andthe central hub portion;

[0021]FIG. 4 is a perspective view of the interface region between thepetal root structure and the central hub portion of the optical spacemirror of FIGS. 1 and 2, illustrating the two hinge assemblies of thesubject invention, and the clevis associated with the latch assembly,which is shown in phantom lines and mounted to the petal root structure;

[0022]FIG. 5 is an exploded perspective view of the onedegree-of-freedom hinge assembly of the subject invention which includesa root mount secured to the petal root and a hub mount secured to thecentral hub portion of the optical space telescope of FIGS. 1 and 2;

[0023]FIG. 6 is an exploded perspective view the two degree-of-freedomhinge assembly of the subject invention which includes a root mountsecured to the petal root and a hub mount secured to the central hubportion of the optical space telescope of FIGS. 1 and 2;

[0024]FIG. 7 is an exploded perspective view of a latch mechanism of thedouble throw latch assembly of the subject invention which includes anaxially advanceable latch shaft configured to engage the clevis on thepetal root structure shown in FIG. 4 upon rotation of the petal aboutthe hinge axis from the stowed position of FIG. 2 to the deployedposition of FIG. 1;

[0025]FIG. 8 is an inverted side elevational view of the double throwlatch assembly of the subject invention in an unlatched position withthe opposed latch shafts disengaged from the clevis disposedtherebetween; and

[0026]FIG. 9 is an enlarged, localized and inverted side elevationalview of the double throw latch assembly of the subject invention in alatched position with the opposed latch shafts in engaged with theclevis disposed therebetween.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Referring now to the drawings wherein like reference numeralsidentify similar structural features of the petal deployment system ofthe subject invention, there is illustrated in FIG. 1 an optical spacetelescope designated generally by reference numeral 110. Optical spacetelescope 10 includes a primary mirror assembly 12 (shown here in adeployed position), a tower 14 that extends from the center of theprimary mirror assembly 12, and a secondary mirror 16 which is mountedatop the central tower 14. The primary mirror assembly or optic 12consists of a hexagonal central hub portion 18 and six petals 20 a-20 fthat are independently hinged to the central hub portion 18.

[0028] As illustrated in FIG. 2, three of the petals 20 a, 20 c and 20 eare hingedly mounted for stowage in an aft position and three of thepetals 20 b, 20 d and 20 f are mounted for stowage in a forwardposition. Each petal 20 a-20 f has a launch latch strut 22 associatedtherewith that secures the petal in a stowed position. Each petal 20a-20 f has a figure-controlled reflective surface 24 that is formed fromfused silica facesheets and a housing 26 formed from a light-weightcarbon composite material. The shape of the reflective surface 24 ofeach petal 20 a-20 f is controlled by a plurality of figure controlactuators (not shown) positioned within the petal housing 26.

[0029] The radially inward end of each petal housing 26 forms atriangular petal root structure 30 that supports a pair of hingeassemblies 100, 200 which are discussed in greater detail hereinbelow.Each of the petals 20 a-20 f is operatively connected to the central hubportion 18 of primary mirror assembly 12 by two hinge assemblies 100,200 (see FIG. 4). The petal root structure 30 also supports a clevis 50that forms part of a latch assembly 300 operatively associated with thecentral hub portion 18 for engaging the clevis 50 upon movement of apetal from the stowed position of FIG. 2 to the deployed position ofFIG. 1.

[0030] Referring to FIG. 3, each paired set of hinges assemblies 100 and200 define a common hinge line or axis A about which the petalassociated therewith rotates, and along which thermal expansion andcontraction, as well as rigid movement of the petal structure isaccommodated. The latch assembly 300 defines a latch line or axis B thatis spaced from and parallel to the hinge axis A. The latch assembly 300is adapted and configured to accommodate thermal expansion andcontraction, as well as rigid axial movement of the petal structurealong latch axis B.

[0031] The One Degree of Freedom Hinge Assembly

[0032] Referring to FIGS. 3 through 5, hinge assembly 100 is a onedegree of freedom hinge assembly (LDOF) in that it is adapted andconfigured to afford the petal associated therewith freedom of rotationabout the petal hinge axis. Hinge assembly 100 includes a root mount 110secured to the mounting surface 32 of the root structure 30 of a petal20, and a hub mount 120 secured a mounting surface 34 of the central hubportion 18 of primary mirror assembly 12.

[0033] The root mount 110 is defined by a base 112 and pair ofupstanding trusses 114 a and 114 b. The base 112 is secured to themounting structure 32 of the petal root structure 30 by a plurality offasteners 35. The trusses 114 a and 114 b have respectivehemi-cylindrical channels 116 a and 116 b for accommodating an axialhinge shaft 130. Channels 116 a and 116 b are further defined andenclosed by corresponding channeled root mount caps 118 a and 118 b thatare secured to the trusses 114 a and 114 b, respectively, by fasteners37.

[0034] Hinge shaft 130 is secured to the root mount 110 of hingeassembly 100 by a pair of axially spaced apart woodruff keys 140 a and140 b. More particularly, woodruff keys 140 a and 140 b are seated incorresponding slots 115 a and 115 b that are respectively formed in thechannels 116 a and 16 b of trusses 114 a and 114 b. The two keys 140 aand 140 b are positioned to engage complementary slots (not shown) thatare formed in hinge shaft 130 to secure the orientation of the shaft 130with respect to the root mount 110.

[0035] Hinge shaft 130 is divided into two sections 130 a, 130 bseparated by an annular collar 132. The first shaft portion 130 a ofhinge shaft 130 extends laterally from hinge assembly 100 and issupported within a stabilizing block 160 is fixedly secured to themounting surface 34 of hub portion 18, as best seen in FIG. 4. Thesecond shaft portion 130 b supports four axially spaced apart angularcontact bearings 150 a-150 e which are axially aligned and retainedbetween the annular collar 132 and a retaining collar 128. The angularcontact bearings 150 a-150 d are preferably formed from silicon nitride,and do not require lubrication. Each angular contact bearing 150 a-150 dhas relatively movable inner and outer races 152 and 154. The inner race152 of each bearing is tightly fit onto the first shaft portion 130 b ofhinge shaft 130.

[0036] The hub mount 120 of hinge assembly 100 is defined by a base 122and a pair of upstanding trusses 124 a and 124 b. The base 122 issecured to the mounting structure 32 of the petal root structure 30 by aplurality of fasteners 35. The trusses 124 and 124 b transition into acylindrical housing 126. The outer race 154 of each of the angularcontact bearings 150 a-150 d is tightly fit within the cylindricalhousing 126 of hub mount 120. The four contact bearings are enclosedwithin the cylindrical housing 126 by a retainer ring 125 that issecured to the end of the housing 126 by plurality of threaded fasteners137.

[0037] In operation, when a petal 20 a-20 f of primary mirror assembly12 is moved from the stowed position of FIG. 2 to the deployed positionof FIG. 1, the relatively movable inner and outer races 152 and 154 ofeach angular contact bearing 150 a-150 d affords rotational movement ofthe root mount 110 relative to the hub mount 120 along the axis of thehinge shaft 130. Hinge assembly 100 constrains all other movementrelative to the hinge axis.

[0038] The Two Degree of Freedom Hinge Assembly

[0039] Referring to FIGS. 3, 4 and 6, hinge assembly 200 is a twodegree-of-freedom hinge assembly (2DOF) in that it adapted andconfigured to afford the petal associated therewith freedom of rotationabout the petal hinge axis, as well as freedom to expand and contractthermally, and move rigidly along the petal hinge axis in africtionless, unconstrained manner. Hinge assembly 200 includes a rootmount 210 secured to the mounting surface 32 of the root structure 30 ofa petal 20, and a hub mount 220 secured to the mounting surface 34 thecentral hub portion 18 of the primary mirror assembly 12. The root mount210 is defined by a base 212 and pair of upstanding trusses 214 a and214 b. The base 112 is secured to the mounting structure 32 of the petalroot structure 30 by a plurality of fasteners 35. The trusses 214 a and214 b have respective hemi-cylindrical channels 216 a and 216 b foraccommodating an axial hinge shaft 230. Channels 216 a and 216 b arefurther defined and enclosed by corresponding channeled root mount caps218 a and 218 b that are secured to the trusses 214 a and 214 b,respectively, by fasteners 37.

[0040] Hinge shaft 230 is supported by the root mount 210, and moreparticularly is seated within the channels formed by trusses 214 a, 214b and root mount caps 218 a, 218 b. A unique bearing assembly 250, thatenables hinge assembly 200 to provide two degrees of freedom, isoperatively associated with hinge shaft 230. Bearing assembly 250includes a cylindrical bearing cage 240 that is preferably formed fromPTFE, and retains a plurality of ball bearings 245 formed from siliconnitride. The ball bearings 245 are arranged in a splined pattern.Bearing assembly 250 father includes a cylindrical inner bearing race252 and a cylindrical outer bearing race 254. The inner bearing race 252is intimately engaged with hinge shaft 230, retained by the annularshaft collar 232. Similarly, the outer bearing race 254 is intimatelyengaged with hub mount 220.

[0041] The hub mount 220 of hinge assembly 100 is defined by a base 222and a pair of upstanding trusses 224 a and 224 b. The base 222 issecured to the mounting structure 32 of the petal root structure 30 by aplurality of fasteners 35. The trusses 224 and 224 b transition into acylindrical housing 226. The outer cylindrical race 254 of bearingassembly 250 is accommodated within the cylindrical housing 226 of hubmount 220.

[0042] In operation, when a petal 20 of primary mirror assembly 12 ismoved from the stowed position of FIG. 2 to the deployed position ofFIG. 1, the relatively movable inner and outer races 252 and 254 ofbearing assembly 250 afford rotational and linear movement of the rootmount 210 relative to the hub mount 220 along the axis of the hingeshaft 230. Consequently, thermal expansion and contraction of the petalroot structure will be accommodated, along with rigid movement of theroot structure along the petal hinge axis A in a frictionless,unconstrained manner. Hinge assembly 200 constrains all other movementrelative to the hinge axis.

[0043] The Double Throw Latch Assembly

[0044] Referring now to FIGS. 3, 4 and 7 through 9, latch assembly 300is a double throw latch assembly that is extremely stable in that itexhibits high stiffness and low hysterisis when subjected to operationalloads experienced during deployment. Latch assembly 300 is adapted andconfigured to afford the petal associated therewith freedom to expandand contract thermally, and move rigidly along the latch axis B. Morespecifically, latch assembly 300 is designed to constrain fourdegrees-of-freedom and allow unconstrained motion relative to the hingeaxis A in two degrees-of-freedom. That is, the latch assembly 300constrains the petal rotational degree-of-freedom about the hinge axisA, as well as the lateral degree-of-freedom and two rotationaldegrees-of-freedom about the hinge axis A.

[0045] The latch assembly 300 includes the clevis 50 secured to themounting surface 32 of petal root structure 30 and which defines areception aperture 52 (see FIG. 4). Latch assembly 300 further includesa pair of laterally opposed latches 302 a and 302 b which areoperatively associated with the mounting surface 34 of the central hubportion 18 of primary mirror assembly 12 for engaging the receptionaperture 52 of the clevis 50 upon movement of a petal from the stowedposition of FIG. 2 to the deployed position of FIG. 1.

[0046] Referring to FIG. 7, the laterally opposed latches 302 a, 302 bare identical in construction and function. Each latch includes a latchshaft 330 mounted for linear movement along latch axis B. An actuator360 disposed within a housing 362 fastened to the mounting surface 34 ofcentral hub portion 18 is coupled to the end of each latch shaft 330 byway of a linkage assembly 380. The actuator 360 is adapted andconfigured to facilitate axial advancement of the latch shaft 330relative to the reception aperture 52 of clevis 50. Linkage assembly 380includes a fore link 382 fastened to the end of latch shaft 330, aprimary medial link 383 and an aft coupling 384 operatively associatedwith the actuator drive shaft 364. Medial link 383 is associated withaft coupling 384 through a biasing member 394, and to fore link 383through a pivot member 393.

[0047] Each latch shaft 330 is operatively associated with a bearingassembly 350 that includes a cylindrical bearing cage 340 that is formedfrom PTFE and configured to retain a plurality of ball bearings 345formed from silicon nitride. The ball bearings 345 are seated inrespective apertures and are arranged in a spline pattern. Each bearingcage 340 is disposed between a cylindrical inner bearing race 352 and acylindrical outer bearing race 354. The inner bearing race 352 isintimately engaged with latch shaft 330, retained in part by annularshaft collar 332. The outer bearing race 354 is supported in a hub mount320.

[0048] Hub mount 320 includes a base 322 having upstanding trusses 324 aand 324 b fastened to the mounting surface 34 of the central hub portion18 by a plurality of fasteners 335. The trusses 324 a, 324 b transitioninto a cylindrical housing 326. The outer cylindrical bearing race 354is accommodated within the cylindrical housing 326 of hub mount 320.

[0049] The relatively movable inner and outer races 352 and 354 ofbearing assembly 350 afford rotational and linear movement of the rootmount 310 relative to clevis 50 along the axis of the hinge shaft 330when the petal is in the deployed and latched position. Consequently,thermal expansion and contraction of the petal root structure will beaccommodated by the latch assemblies 300, along with rigid movement ofthe root structure along the hinge axis in a frictionless, unconstrainedmanner relative to the latch axis B.

[0050] With continuing reference to FIG. 7, a tapered bearing 375 ismounted to the free end of latch shaft 330 by a support hub 380 andsecured by a fastener 382. Tapered bearing 375 carries a plurality ofcylindrical rollers 385 adapted and configured to engage the receptionaperture 52 of clevis 50, as discussed in more detail hereinbelow.

[0051] When petals 20 a-20 f of mirror assembly 12 are independentlyrotated into the deployed positions shown in FIG. 1, the opposed latches302 a, 302 b of latch assembly 300 slide past the clevis 50 withoutmaking contact therewith. In the deployed position, the receptionaperture 52 of the clevis 50 on each petal root 30 is aligned with thelatch axis B defined by the opposed latch shafts 330 a, 330 b of latches302 a, 302 b, as best seen in FIG. 8. At such a time, the taperedbearings 375 a, 375 b on the end of latch shafts 330 a, 330 b are spacedfrom the clevis 50. At the appropriate instance, the respective driveshafts 364 a, 364 b of actuators 360 a, 360 b, which are coupled tolatch shafts 330 a, 330 b respectively, are actuated, preferablysimultaneously. This, in turn, causes the tapered bearings 375 a, 375 bto translate axially into engagement with the reception bore 52 ofclevis 50, as best seen in FIG. 9.

[0052] Upon engagement, the rollers 385 within the tapered bearings 375a, 375 b on the end of each latch shaft 330, 330 b contact a receptionbore liner 54 secured within the reception bore 52 of clevis 50. Duringthis engagement, no latching forces are created in the petal rootstructure. The distance through which the latch shafts 330 a, 330 btravel to engage the reception bore 52 of the clevis 50 is relativelysmall compared to their overall length. This ensures that the bearingcage 340 with which each latch shaft 330 a, 330 b is associated does notbecome displaced from its housing defined by hub mount 320.

[0053] The mating forces exerted by the opposed latches 302 a, 302 b onthe clevis 50 are equal and opposite, thus ensuring that a moment willnot be applied to the clevis 50 during engagement. This results in thelow hysterisis and high stiffness exhibited by the latch assembly 300 ofthe subject invention. Specifically, the double throw latch assembly 300of the subject invention exhibits axial stiffness on the order of1,000,000 lbs/in. Consequently, when the opposed latches 302 a, 302 bare engaged, as shown in FIG. 9, the clevis 50 will not rotate andre-seat with the rollers 385 in the bearing 375 a, 375 b on the end ofeach latch shaft 330 a, 330 b.

[0054] Although the subject invention has been described with respect topreferred embodiments, those skilled in the art will readily appreciatethat modifications and changes may be made thereto without departingfrom the spirit or scope of the subject invention as defined by theappended claims. Moreover, while the hinge and latch assembliesdisclosed herein have been described and illustrated with respect to aoptical space telescope such as the NGST, it is envisioned that thesemechanism may be employed in other space based optical systems.

1. A system for deploying the petals of a sectored mirror assembly of anoptical space telescope, the mirror assembly including a central hub anda plurality of petals disposed about the periphery of the central hub,each petal having a petal root independently hinged to the central hub,the system comprising: a) a first hinge assembly including a root mountsecured to a petal root and a hub mount secured the central hub, thefirst hinge assembly affording the petal associated therewith freedom ofrotation about a petal hinge axis; b) a second hinge assembly includinga root mount secured to the petal root and a hub mount secured to thecentral hub, the second hinge assembly affording the petal associatedtherewith freedom of rotation about the petal hinge axis, as well asfreedom to expand and contract thermally, and move rigidly along thepetal hinge axis in a frictionless, unconstrained manner; and c) a latchassembly including a clevis secured to the petal root at a locationspaced from the hinge axis and a pair of laterally opposed latchesoperatively associated with the central hub for engaging the clevis uponrotation of the petal about the hinge axis from a stowed position to adeployed position.
 2. A system as recited in claim 1, wherein the firsthinge assembly includes a first hinge shaft disposed on the petal hingeaxis.
 3. A system as recited in claim 2, wherein the first hinge shaftis secured to the root mount of the first hinge assembly.
 4. A system asrecited in claim 2, wherein the first hinge shaft supports a pluralityof axially spaced apart angular contact bearings.
 5. A system as recitedin claim 4, wherein the angular contact bearings are formed from siliconnitride.
 6. A system as recited in claim 4, wherein the angular contactbearings do not require lubrication.
 7. A system as recited in claim 4,wherein the angular contact bearings are housed within the hub mount ofthe first hinge assembly.
 8. A system as recited in claim 1, wherein thesecond hinge assembly includes a second hinge shaft disposed on thepetal hinge axis.
 9. A system as recited in claim 8, wherein the secondhinge shaft is supported by the root mount of the second hinge assembly.10. A system as recited in claim 8, wherein the second hinge shaft isdisposed within a cylindrical bearing cage.
 11. A system as recited inclaim 10, wherein the bearing cage is formed from 5 PTFE.
 12. A systemas recited in claim 10, wherein the bearing cage retains a plurality ofball bearings.
 13. A system as recited in claim 12, wherein the ballbearings are formed from silicon nitride.
 14. A system as recited inclaim 12, wherein the ball bearings do not require lubrication.
 15. Asystem as recited in claim 12, wherein the bearing cage is disposedbetween an inner bearing race and an outer bearing race.
 16. A system asrecited in claim 10, wherein the bearing cage is housed within the hubmount of the second hinge assembly.
 17. A system a recited in claim 1,wherein the latch assembly is adapted and configured to afford the petalassociated therewith freedom to expand and contract thermally, andrigidly move along a latch axis extending parallel to the hinge axis ina frictionless, unconstrained manner.
 18. A system as recited in claim17, wherein each laterally opposed latch includes a latch shaft mountedfor linear movement along the latch axis.
 19. A system as recited inclaim 18, wherein the clevis defines a reception aperture for receivingthe laterally opposed latch shafts.
 20. A system as recited in claim 18,wherein an actuator is operatively associated with each latch mechanismfor moving the latch shaft thereof into engagement with the clevis. 21.A system as recited in claim 18, wherein each latch shaft is disposedwithin a cylindrical bearing cage.
 22. A system as recited in claim 21,wherein each bearing cage is formed from PTFE.
 23. A system as recitedin claim 21, wherein each bearing cage retains a plurality of ballbearings.
 24. A system as recited in claim 23, wherein the ball bearingsare formed from silicon nitride.
 25. A system as recited in claim 24,wherein each bearing cage is disposed between an inner bearing race andan outer bearing race.
 26. A system as recited in claim 21, wherein eachbearing cage is housed within a hub mount secured to the central hub.27. A system as recited in claim 26, wherein each hub mount includes abase portion and a cylindrical housing portion.
 28. A petal deploymenthinge assembly for connecting a petal of a sectored mirror of an opticalspace telescope to the central hub of the sectored mirror, the hingeassembly comprising: a) a root mount secured to a root of the petal; b)a hub mount secured the central hub; c) an axial hinge shaft secured tothe root mount; and d) a plurality of axially spaced apart angularcontact bearings supported on the hinge shaft and housed within the hubmount for affording rotational movement of the root mount relative tothe hub mount along the axis of the hinge shaft.
 29. A petal deploymenthinge assembly as recited in claim 28, wherein the angular contactbearings are formed from silicon nitride.
 30. A petal deployment hingeassembly as recited in claim 28, wherein the hinge shaft is secured tothe root mount by a pair of axially spaced apart woodruff keys.
 31. Apetal deployment hinge assembly for connecting a petal of a sectoredmirror of an optical space telescope to the central hub of the sectoredmirror, the hinge assembly comprising: a) a root mount secured to a rootof the petal; b) a hub mount secured the central hub; c) an axial hingeshaft supported by the root mount; and d) a cylindrical bearing cagedisposed about the hinge shaft and housed within the hub mount foraffording rotational and axial movement of the root mount relative tothe hub mount along the axis of the hinge shaft.
 32. A petal deploymenthinge assembly as recited in claim 31, wherein the bearing cage isformed from PTFE.
 33. A petal deployment hinge assembly as recited inclaim 31, wherein the bearing cage retains a plurality of ball bearings.34. A petal deployment hinge assembly as recited in claim 33, whereinthe ball bearings are formed from silicon nitride.
 35. A petaldeployment hinge assembly as recited in claim 34, wherein the bearingcage is disposed between an inner bearing race and an outer bearingrace.
 36. A petal deployment latch assembly for securing a petal of asectored mirror of an optical space telescope to the central hub of thesectored mirror, the latch assembly comprising: a) a clevis secured to aroot of a petal and defining a reception aperture; and b) a pair oflaterally opposed latches operatively associated with the central hubfor engaging the reception aperture of the clevis upon movement of thepetal from a stowed position to a deployed position.
 37. A petaldeployment latch assembly as recited in claim 36, wherein each laterallyopposed latch includes a latch shaft mounted for linear movement along alatch axis.
 38. A petal deployment latch assembly as recited in claim36, wherein the latch assembly is adapted and configured to afford thepetal associated therewith freedom to expand and contract thermally, andmove rigidly along the latch axis.
 39. A petal deployment latch assemblyas recited in claim 37, wherein an actuator is operatively associatedwith each latch for moving the latch shaft thereof into engagement withthe clevis.
 40. A petal deployment latch assembly as recited in claim37, wherein each latch shaft is disposed within a cylindrical bearingcage.
 41. A petal deployment latch assembly as recited in claim 40,wherein each cylindrical bearing cage is formed from PTFE.
 42. A petaldeployment latch assembly as recited in claim 41, wherein eachcylindrical bearing cage retains a plurality of ball bearings.
 43. Apetal deployment latch assembly as recited in claim 42, wherein the ballbearings are formed from silicon nitride.
 44. A petal deployment latchassembly as recited in claim 43, wherein each bearing cage is disposedbetween an inner bearing race and an outer bearing race.
 45. A petaldeployment latch assembly as recited in claim 40, wherein each bearingcage is housed within a hub mount secured to the central hub.
 46. Apetal deployment latch assembly as recited in claim 45, wherein each hubmount includes a base portion and a cylindrical housing portion.
 47. Apetal deployment latch assembly for securing a petal of a sectoredmirror of an optical space telescope to the central hub of the sectoredmirror, the latch assembly comprising: a) a clevis secured to a root ofa petal and defining a reception aperture; and b) a pair of laterallyopposed latches operatively associated with the central hub for engagingthe reception aperture of the clevis upon movement of the petal from astowed position to a deployed position, each latch including: i) a latchshaft mounted for linear movement along a latch axis; ii) a cylindricalbearing cage surrounding the latch shaft; and iii) a hub mount securedto the central hub and housing the bearing cage in such a manner so thatthe petal associated with the latch assembly is afforded freedom toexpand and contract thermally, and move rigidly along the latch axis ina frictionless, unconstrained manner.
 48. A petal deployment latchassembly as recited in claim 47, wherein each hub mount includes a baseportion and a cylindrical housing portion.
 49. A petal deployment latchassembly as recited in claim 47, further comprising an actuatoroperatively associated with each latch for linearly moving the latchshaft thereof into engagement with the clevis.
 50. A petal deploymentlatch assembly as recited in claim 47, wherein each bearing cage isformed from PTFE.
 51. A petal deployment latch assembly as recited inclaim 47, wherein each bearing cage retains a plurality of ballbearings.
 52. A petal deployment latch assembly as recited in claim 51,wherein the ball bearings are formed from silicon nitride.
 53. A petaldeployment latch assembly as recited in claim 47, wherein each bearingcage is disposed between an inner bearing race and an outer bearingrace.